Field of the Invention
The present invention relates to a sheet member supply device and an image forming apparatus, such as a copying machine, that includes the sheet member supply device.
Description of the Related Art
In an image forming apparatus such as a copying machine, a printer or a facsimile, a supply device of a sheet member such as a sheet is provided. In the sheet member supply device, sheet members stacked on a storage portion are often separated and supplied one by one from the uppermost layer. Conventional technologies related to such a sheet member supply device are disclosed in patent documents 1 to 3.
In each of the sheet member supply devices disclosed in Japanese Unexamined Patent Application Publication Nos. 2007-269462, 2010-105768 and 5-58480, the downstream side in a sheet member supply direction of a sheet member stacking plate in which sheet members are stacked on the upper surface is displaced upward, and thus the uppermost layer of the sheet members makes contact with, from below, a pickup roller for feeding out the sheet member. In these sheet member supply devices, a technology for preventing the sheet member stacking plate from being unintentionally ally displaced downward is proposed.
The sheet member supply device in an image forming apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2007-269462 includes a one-way crutch for regulating the unintentional downward displacement of the sheet member stacking plate. In this way, it is possible to apply a force acting upward to the sheet member stacking plate by constantly providing an appropriate force.
The sheet member supply device in an image forming apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2010-105768 includes: a crutch gear which is formed with a planetary gear mechanism for regulating the unintentional downward displacement of the sheet member stacking plate; and a stopper which is engaged therewith. In this way, the lowering of the sheet member stacking plate is regulated.
The sheet member supply device in an image forming apparatus disclosed in Japanese Unexamined Patent Application Publication No. 5-58480 includes; a worm gear for regulating the unintentional downward displacement of the sheet member stacking plate; and a worm wheel engaged therewith. in this way, a brake action between the worm gear and the worm wheel is utilized, and thus it is possible to hold the posture of the sheet member stacking plate.
However, in the conventional technology disclosed in Japanese Unexamined Patent Application Publication No. 2007-269462, in addition to one-way crutches for motive power transmission and deceleration, another one-way crutch needs to be provided, with the result that the number of components is disadvantageously increased.
In the conventional technology disclosed in Japanese Unexamined Patent Application Publication No. 2010-105768, since the stopper and its nail directly receive the load of a stack of sheet members, without consideration given to sufficient strength, they may be disadvantageously damaged. Disadvantageously, even when they are not damaged, it is likely that the stopper and its nail are elastically deformed, and that thus the sheet member stacking plate is displaced downward. Even when the stopper and its nail are designed with consideration given to sufficient strength, the thickness of the nail may be increased in a circumferential direction of the crutch gear, with the result that there is a concern that the accuracy of a stop position is lowered.
Disadvantageously, in the conventional technology disclosed in Japanese Unexamined Patent Application Publication No. 5-58480, since the brake action (self-holding function) is exerted by a friction between the worm gear and the worm wheel, it is likely that variations in friction force are produced by the change of usage environment, aging degradation or the like and that thus the sheet member stacking plate is displaced downward.
The present invention is made in view of the foregoing points, and an object thereof is to provide a sheet member supply device that can reduce the unintentional downward displacement of the sheet member stacking plate and an image forming apparatus.